The manufacture of microelectronic devices is often very complex, requiring a plurality of processing steps to be performed utilizing a variety of fluids, liquids and/or solutions. Further, due to the nature of microelectronic devices, the tolerance range for any degree of error or nonconformance to manufacturing standards is extremely low. Variability of treatment processes for microelectronic devices is introduced by the difficulty to control concentration and the temperature of chemicals used in the processes, particularly when comparing batch to batch uniformity of the treatment processes.
Various techniques have been used to attempt to improve consistency of treatment processes. For example, U.S. Pat. No. 6,261,845 to Verhaverbeke, et. al. describes systems and methods of determining the concentration of chemicals in a wet processing stream where the wet processing stream is formed from two or more liquid streams having known chemical concentrations. This process determines the concentration of each chemical by calculation based on the instantaneous or real time flow rate of the liquid streams during a given time interval. The thus calculated concentration of a wet processing stream is stated to be used to calculate the exposure time of the same wet processing stream with the semiconductor substrates. This system relies on the reliability of flow measuring devices to determine relative concentration of ingredients. The rate of flow in these systems is not controlled, but only monitored. The flow rate is thus subject to line pressure variations. There additionally is no indication that presumed flow rates are checked in any manner. Based on this calculated concentration level, the exposure time of the substrate to the wet process stream is calculated, and is stated to capable of being adjusted based on temperature and/or concentration variation. See Column 9, lines 19-23. The patent goes on to describe an example whereby a measured etch rate was plotted against measured and calculated HF concentrations. See Table 1. The Example does not report whether variation in temperature of the process bath was measured during the experiment. On the basis of this data, the Patentees concluded that the calculated HF concentration had less variation than the actually measured concentration, and that the resulting graph conformed to what the skilled artisan would have expected for a graph showing etch rate verses concentration of HF. See column 17, lines 1-4.
United States Patent Application Publication No. 2003/0094196 describes a system for advanced process control for immersion processing that is capable of providing a desired blend of at least two chemicals to an immersion bath as well as methods of treating substrates immersively. The system is capable of producing a blend with one or more desired properties extremely accurately due at least in part to the capability of the system to monitor at least one property of the blend or at least one parameter of the immersion process and to utilize the information gathered to provide dynamic closed-loop feedback control of one or more process parameters known to relate to the same.
It would be desirable to provide an immersion chemical processing system that is in particular capable of carrying out a treatment process with a low variability from batch to batch and from tool to tool.